The present invention is directed to the prevention of carbon formation in gas phase reforming catalytic operations at temperatures above 900.degree. F. Reforming is the conversion of high molecular weight hydrocarbons, such as naphtha and crude oil by reaction with steam to lower molecular weight species, such as methane or the conversion of any hydrocarbon to carbon oxides and hydrogen. A particular example is the reforming of methane to hydrogen and the oxides of carbon. Hydrocracking is a form of reforming which includes the conversion of heavier hydrocarbons to lower molecular species by reaction with hydrogen.
The catalytic reforming of natural gas, refinery gases, liquefied petroleum gases and naphthas is practiced commercially for the production of syngases or "rich" gases which are used for the production of hydrogen, ammonia, methanol and other chemicals. Conventionally, the reforming reaction occurs on a nickel-type catalyst in the presence of steam at temperatures ranging from the reformer inlet of 900.degree. F to the outlet of approximately 1600.degree. F. Excess steam over the stoichiometric quantity required for the reforming reaction, is used not only to achieve a high degree of conversion to syngas, but also to assist in the prevention of carbon formation from the syngas produced or from a syngas containing hydrogen and carbon oxides which may be added as reactants in the reforming process.
Sulfur is regarded as a catalyst poison in the reforming operation. It is believed necessary to reduce the total quantity of sulfur present to levels substantially below 1 ppm if not eliminate them. Higher concentrations of sulfur have been noted to cause a reduction in the activity of the catalyst which leads to carbon formation from the hydrocarbon feed materials. Once formed, carbon catalyzes its own formation. For example, in the conversion of naphtha to a syngas consisting mainly of hydrogen, carbon oxides to methane, catalytic reforming is limited to a 400.degree. F end point feed stock which can contain no more than about 0.2 ppm sulfur using a minimum of about 1.4 pounds of steam per pound of feed stock. Of this total steam, excess over the stoichiometric quantity required for reforming, and which is used to control carbon formation, results in a loss of thermal efficiency for the process and added costs for its recovery and separation as a condensate from the product gas.